1. Field of the Invention
The present invention concerns a method to control a medical apparatus, in particular for generation of images, which are optimally free of movement artifacts, of a tissue of the patient who moves due to cardiac activity and/or breathing, and/or for radiation therapy of a tissue of the patient who is moving due to cardiac activity and/or breathing. The invention also concerns an installation with such a medical apparatus and a computer to execute such a method, as well as a non-transitory data storage medium embodying programming instructions (commands) to execute such a method.
2. Description of the Prior Art
In the examination of tissue of a patient with an imaging apparatus, for example with an x-ray computed tomography apparatus, multiple 2D x-ray projections of the tissue are acquired respectively from different projection directions, most often during advancement of the tissue of the patient relative to the x-ray acquisition system of the x-ray computed tomograph. The goal of the examination is the generation of qualitatively high-grade and relevant images of the tissue based on the 2D x-ray projections, which images frequently form the basis for a medical diagnosis.
If tissue in the region of the torso of the patient is examined, the movement of such tissue that is caused by cardiac activity or breathing of the patient should also be taken into account in the generation of images of this tissue in order to be able to acquire high-quality images of the tissue that are free of movement artifacts.
For example, in the imaging of the heart itself as the tissue to be examined, in order to avoid such movement artifacts in the reconstructed slice images and 3D images of the heart, in the reconstruction of slice images and 3D images that takes place based on the acquired 2D x-ray projections of the heart, it is always sought to use only those 2D x-ray projections that have been acquired in the cardiac phase of the cardiac cycle of the patient in which the heart has performed practically no movement. It is typical to record an electrocardiogram (EKG) of the heart of the patient to determine the cardiac cycle of the heart of the patient.
For the generation of slice images and 3D images of the heart, 2D x-ray projections of the heart are normally acquired with parallel recording of the electrocardiogram over multiple cardiac cycles, and only thereafter is a selection made as to the 2D projections that are suitable for the reconstruction (based on the electrocardiogram). For this reason, this type of method is called a retrospective method.
In an alternative procedure, 2D x-ray projections of the heart are likewise acquired over multiple cardiac cycles, but based on an electrocardiogram acquired in parallel, acquisition of the respective projections takes place only when the heart is located in a cardiac phase at which it performs practically no movement. This procedure has the advantage that the patient is exposed to a lower dose of x-ray radiation.
If the patient has a low and uniform heart rate i.e., a uniform cardiac cycle, such as below 60 bpm (beats per minute), a relatively short time period around the 60% position of the RR interval can be identified by analysis of the RR interval in the EKG, in which time period 2D x-ray projections can be acquired in each cardiac cycle, for example. In this context, a “pulsing window” is established, which is a time window in which x-ray radiation is applied. Generally, it is preferable for the pulsing window to substantially coincide with the rest phase of the heart. Under such circumstances, a low dose of x-ray radiation for the acquisition of 2D x-ray projections from different projection directions that is required for the reconstruction of images of said heart is applied to the patient. A high image quality is simultaneously achieved.
The imaging procedure also can be implemented under consideration of breathing movements. A breathing belt is frequently used that embodies a motion sensor and is placed on the patient in the chest area to detect breathing movements. The detected breathing cycle is taken into account in the imaging.